1. Field of the Invention
The present invention relates to a self-extinguishing thermoplastic composition comprising a thermoplastic polycondensation product and to a process for the preparation thereof.
2. Discussion of Related Art
Formulations of halogen compounds, and in most cases these compounds being in combination with antimony trioxide, are recommended as flame retardants for the manufacture of flameproof polycondensation products. Typical representatives of such halogen compounds are perbrominated aromatics, such as decabromodiphenyl oxide, polymers thereof, such as polytribromophenylene oxide, as well as, for example, perchloropentacyclodecane. The use of such products as flame retardants has been described in U.S. Pat. No. 3,418,267, German Published Applications DE-AS 1,694,494 and DE-AS 1,931,387, German Laid-Open Application DE-OS 2,544,219, and German Patent DE 2,937,379 C 2.
In spite of advances in the art afforded by the utilization of these halogen compounds as flame retardants, their use is accompanied by considerable drawbacks. Such drawbacks have been dealt with in detail in British Patent 0044 419 B1 and in German Patent 3,208,486 C 2. An especially grave disadvantage resides in that when using perbrominated aromatics, such as decabromodiphenyl oxide or decabromodiphenyl, toxic compounds are formed during their combustion, such as dioxins and furans, so that in the case of a fire, grave injuries can occur.
In addition to the halogen compounds, it is also known to use elemental red phosphorus for rendering thermoplastics, particularly polyamide, flameproof. This mode of operation is set forth in German Published Application DE-AS 1,173,641 and U.S. Pat. No. 3,951,908.
Here again, a number of drawbacks must be tolerated, such as the effect on the color and electrical values. British Patent 0044 419 B1 provides information on these aspects.
Finally, a number of nitrogen-containing compounds are utilized as flame retardants in thermoplastics. These involve melamine, as well as melamine derivatives. Such have been suggested, inter alia, in U.S. Pat. No. 4,263,203, German Patent DE 2,937,379 C 2, British Patent 0044 419 B1, and German Published Application DE-AS 1,694,254. As disclosed in the specifications of the aforementioned patents, nitrogen-containing compounds exhibit a number of advantages over the previously mentioned products.
However, in most cases, processing stability is inadequate, especially when the higher-melting polyamide and polyester types, such as polyamide 6,6 and polybutylene terephthalate, are rendered flameproof. In particular, nitrogen-containing compounds are unsuitable for mineral- and glass-fiber-reinforced polyamide and polyester synthetic resins, to be utilized in the industrial field. Besides lacking temperature stability, such nitrogen-containing flame retardants have the drawback in that they do not melt with the polymer melt but rather are present therein only as extremely fine particles. In the usual case, a dispersant must be additionally used in order to obtain a maximally fine, uniform distribution. This situation results in a decrease in the mechanical values during the use of these flame retardants, especially in the impact resistance property.
The advantage displayed by the use of melamine cyanurate, as compared with melamine in accordance with the patent specifications, resides in a reduction in the so-called plate-out due to the sublimation of melamine at processing temperatures. However, the use of melamine cyanurate does lead to increased dripping. This makes it even difficult to stay within the customary flame retardance test UL 94-V0 (in accordance with testing standard by Underwriters Laboratories Inc., dated Feb. 1, 1974).
Melamine display greater temperature stability than melamine cyanurate. However, practical application thereof is hindered, in addition to the aforementioned tendency toward sublimation leading to plate-out, it is also hindered by the lower hydrolysis stability of melamine. When boiling melamine-treated polyamide test rods, the flame retarding effect which was initially present, is diminished.
German Patent 3,208,486 C 2 describes the use of a reaction product of cyanuric acid with 2 to 2.35 moles of melamine and, respectively, whereby melamine derivatives having the above-described deficiencies are to be avoided. However, the admixture rates in order to attain self-extinguishing properties in accordance with UL 94 are relatively high. Furthermore, the data relate especially to polyamide 6,6 rather than to glass-fiber-reinforced thermoplastics, of which the flameproofing thereof has gained increasing importance.